The absorptance characteristics of metal mirrors, with thin dielectric overcoats on their surface, have been measured at angles of incidence from 0 to 89°, for both s and p-polarizations. The mirrors tested are silver overcoated with ThF4, and aluminum overcoated with MgF2. To understand the experimental results requires the use of models incorporating thin film theory. Estimations of parameters, such as film thickness, can be made by varying parameters within the model until the best fit with the experimental data is obtained. This paper presents the results of model comparisons with the glancing incidence data. In addition, thin film designs for overcoated mirrors with enhanced reflectivity at glancing incidence are discussed.